Anti-tracking feature for rock bits

ABSTRACT

The harmful effects of tracking are reduced for a drill bit having roller cones with at least one of the outermost rows of active teeth containing one or more teeth having a height that does not extend to the height of at least one of the outermost rows on another roller cone on the bit. The crest on this tooth may have a length in a circumferential direction that is wider than an overall width of the tooth in the outer to inner direction. The invention may be used on any cutter row, not just the outermost row. The design may be used on a different roller cone or row, or more than one cutter row. The anti-tracking feature may be located between the leading and trailing edges of the tooth on one or more roller cones.

This application claims priority to U.S. Provisional Pat. App. No. 61/046,508, filed on Apr. 21, 2008, and i s incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates in general to drill bits and, in particular, to an improved system, method, and apparatus for reducing the harmful effects of tracking with drill bits.

2. Description of the Related Art

A roller cone earth-boring drill bit has a number of cones, typically three, each of which is rotatably mounted to a bearing pin. Each cone rotates about its axis when the bit body rotates around the bit axis. The cones have cutting elements, often in rows, which may be teeth integrally formed in the cone metal, or tungsten carbide inserts pressed into mating holes in the cone metal.

Each cone has an outermost or heel row near a gage surface of the cone and one or more inner rows. One or more of the cones have cutting elements located near or on the nose of the cone. In some cases the cutting elements in the adjacent row closest to the heel row will be staggered or alternate with the cutting elements in the heel row.

The inner rows of each cone are arranged at different distances from the bit axis for cutting different portions of the borehole bottom. Normally at least two of the cones have heel rows that are located at substantially the same distance from the bit axis. When all three cones are rotated into a single section plane, the heel row cutting elements superimpose or overlap (at least partially) on one another. The inner rows are normally spaced at different distances from the bit axis and thus provide single row coverage on the remaining portions of the borehole bottom. When the cones are rotated about their axes, the rows of teeth make indentations on the borehole bottom. When the teeth fall into the same indentations on consecutive rotations, a detrimental process commonly referred to as “tracking” results.

With tracking, one or more rows of the cutting elements on one or more cones tend to fall into the same holes in the borehole bottom, thereby building up ridges on the bottom. These ridges are detrimental because they grow in height until they contact the supporting metal of the cone. This lowers the unit load on the cutting elements and causes undesirable erosion and wear.

In the prior art, attempts to reduce tracking typically consist of methods to vary pitch (i.e., the distance between center lines of the cutting elements) on overlapping heel rows on different cones, and/or within a single row on one cone. For example, a common approach uses a combination of a closely-spaced heel row on one cone and a wider pitch (e.g., 1.5 times the close pitch) on an overlapping heel row on another cone. A wider pitch tends to break up the ridges that form between the impressions made by the more closely-spaced heel row cutting elements. While workable, a wider pitch means fewer cutting elements and less durability. On the other hand, the more closely-spaced row is more likely to ball in softer, sticky formation. Thus, an improved solution for overcoming tracking without sacrificing bit life or penetration rate would be desirable.

SUMMARY OF THE INVENTION

Embodiments of a system, method, and apparatus for reducing the harmful effects of tracking with drill bits are disclosed. A roller cone has a plurality of active teeth arranged generally in circumferential rows. At least one of the outermost rows contains one or more teeth having a projection that does not extend to the height of at least one of the outermost rows on another roller cone on the bit. This row is designed to engage and remove the formation that remains as a result of the uncut formation from the space between adjacent active teeth of the other roller cone. The crest on this tooth may have a length in a circumferential direction that is wider than an overall length of the tooth in the outer to inner direction.

The cutter design removes the peak of the uncut bottom left by the other roller cones, significantly removing the depth of the pocket and allowing the other roller cones to continue to cut with their crests rather than with the sides of their active teeth or with their cones. Tracking is reduced regardless of the tooth count in the other rows or weight on bit. The invention may be used on any cutter row that shares a common bit diameter and not just the outermost row. Moreover, the invention may be used on a different roller cone or row, or more than one cutter row that shares a common bit diameter.

The teeth on each cutter may be a combination of full projection cutting elements dispersed with any of the anti-tracking or tracking limiter elements described herein. The anti-tracking feature may be located between the leading and trailing edges of the tooth on one or more roller cones. The anti-tracking feature may also be formed more than once and in different locations on any tooth or combination of teeth. Furthermore, the invention may be used with gage cutting features, such as a “bar trimmer” aligned with the cone centerline and also at an angular position.

Alternatively, a heel row may have a high count of teeth on a roller cone with teeth configured at a depth that is shorter than a formation contact depth for active teeth on the other roller cones. The heel row also may be milled with narrow slots to define teeth having properties and features as described herein.

The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the present invention, taken in conjunction with the appended claims and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the features and advantages of the present invention, which will become apparent, are attained and can be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof that are illustrated in the appended drawings which form a part of this specification. It is to be noted, however, that the drawings illustrate only some embodiments of the invention and therefore are not to be considered limiting of its scope as the invention may admit to other equally effective embodiments.

FIG. 1 is a sectional view illustrating a portion of an earth boring bit constructed in accordance with the invention;

FIG. 2 is an enlarged isometric view of one embodiment of a heel portion of a roller cone for the bit of FIG. 1 and is constructed in accordance with the present invention;

FIG. 3 is an enlarged isometric view of another embodiment of a roller cone constructed in accordance with the present invention;

FIG. 4 is another isometric view of the roller cone of FIG. 3 on a bit and is constructed in accordance with the present invention;

FIG. 5 is an enlarged isometric view of still another embodiment of a roller cone constructed in accordance with the present invention;

FIG. 6 is another isometric view of the roller cone of FIG. 5 on a bit and is constructed in accordance with the present invention;

FIG. 7 is an enlarged isometric view of yet another embodiment of a roller cone constructed in accordance with the present invention;

FIG. 8 is a rear view of the roller cone of FIG. 7 and is constructed in accordance with the present invention;

FIG. 9 is an isometric view of another embodiment of a roller cone on a bit and is constructed in accordance with the present invention;

FIG. 10 is another isometric view of the roller cone of FIG. 9 and is constructed in accordance with the present invention;

FIG. 11 is an enlarged sectional view of one embodiment of a bit illustrating a cutting profile thereof relative to a borehole;

FIG. 12 is a schematic side view illustrating effective depth of cut in accordance with the invention;

FIG. 13 illustrates top views of various embodiments of tooth geometries in accordance with the invention; and

FIGS. 14 and 15 depict rear and isometric views of embodiments of a cone with anti-tracking features in accordance with the invention, and is shown with the active teeth of other cones projected onto the cone.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1-15, embodiments of an improved system, method, and apparatus for reducing the harmful effects of tracking with drill bits are disclosed. One embodiment of a bit 11 (FIG. 1) has a body 13 with a threaded shank 15 on its upper end for connection to a drill string (not shown). Body 13 typically has three bit legs 17 (only one shown), and each leg 17 has a depending bearing pin 19. Each bearing pin 19 inclines downward and inward toward an axis 20 of rotation of body 13. Each bearing pin 19 has a cylindrical surface 21 that is concentric with a bearing pin axis 23. A roller cone 29 is mounted to each pin 19 and has an axial cavity with a cylindrical portion 31 that fits around bearing surface 21 of pin 19. Roller cone 29 rotates on pin 19 about its roller cone axis, which coincides with bearing pin axis 23.

Each roller cone 29 has a plurality of cutting elements 36 (FIG. 1) on its exterior. Cutting elements 35 may be formed as steel teeth milled into the exterior surface of the body of cone 29 with or without hardfacing. Alternatively, cutting elements 36 may comprise tungsten carbide inserts press-fitted into holes in the body of cone 29, as integral protrusions extending from cone 29, or other configurations known to those skilled in the art. Cone 29 is retained conventionally on bearing pin 19, which in this example is by a plurality of balls 37. Balls 37 engage mating grooves formed in cone 29 and on bearing pin 19. Lubricant passages 39 supply lubricant or grease to the spaces between cylindrical surfaces 21, 31 and between thrust faces. A pressure compensator 41 reduces the pressure differential between the lubricant within passages 39 and drilling fluid pressure on the exterior of bit 11.

Referring now to FIGS. 2, 14 and 15, some embodiments of roller cone 29 have a plurality of “passive” elements (e.g., teeth) 35 that reduce the harmful effects of tracking. Teeth 35 may be formed integrally on cone 29 and arranged generally in circumferential rows 51, 53. Each of the teeth 35 includes an outer end 55 and an inner end 57 that define a length 58, a pair of flanks 59, 61 (i.e., leading edge and trailing edge, respectively) and a crest 63 at which the ends 55, 57 and flanks 59, 61 converge. The outermost row 51 contains one or more teeth 35 having a height 65 that does not extend to the height 67 (shown superimposed) of the active teeth 36 (FIGS. 14 and 15) on at least one of the outermost rows the roller cones. Row 51 is designed to engage and remove the formation that remains as a result of the uncut formation left behind between tooth impressions of the other roller cone or cones. The crest 63 on this tooth 35 has a width 69 in a circumferential direction that is wider than an axial length 58 of the tooth 35 in the axial direction.

The embodiments of FIGS. 2, 14 and 15 are shown on the row that is used to remove the outermost portions of the borehole where at least two other roller cones on the bit have rows of teeth that are used to remove the same outer portion of the formation. As described above, one cutter (i.e., roller cone 29) has a row 51 of teeth 35 that are shorter (compare height 65 to height 67) than the same row of active teeth 36 on the other roller cones. The circumferential width 69 (i.e., in a generally angular direction with respect to the axis of the cone) of each tooth 35 on row 51 is shown longer than the crest width 73 (shown superimposed) of active teeth 36 on the outermost rows on the other roller cones. The inner-to-outer end length 58 on row 51 is shown shorter than that of the respective length 75 of active teeth on other rows 53. This improved cutter design removes the peak of the uncut bottom left by the active teeth of the other roller cones, significantly reducing the depth of the valleys and allowing the other roller cones to continue to cut with their crests and less contact on the sides of their active teeth or cone shell.

Although heel tracking can be reduced by increasing the tooth count, such a configuration results in an increased tendency to ball, with less effective projection and lower rate of penetration. Furthermore, it is still subject to tracking although at a smaller distance between impressions. With the present invention, the detrimental effect of tracking is reduced even with low tooth counts in the other rows. The invention may be used on any cutter row that shares a common distance from the center of the bit and not just the outermost row as shown. Moreover, the invention may be used on multiple cutter rows, or within a single cutter row that has the same distance from the center of the bit.

In addition, the teeth on each cutter may be a combination of full-length cutting elements dispersed with any of the anti-tracking (or, tracking limiter) elements described herein. For example, as shown in FIGS. 3 and 4, a tooth 101 on each cutter 129 may comprise a combination of a full-height, active cutting element integrally morphing into an anti-tracking element 103 (e.g., having a shorter radial height). For simplicity of illustration, some of the drawings are shown without an innermost row of teeth. The morphed portion 103 may be curved and located on the leading edge of the tooth, or on the trailing edge of the tooth. FIG. 13A depicts a top view of tooth 101. Morphed portion 103 tapers not only radially with respect to the axis of cone 129 (FIGS. 3 and 4), but the crest also tapers in width in the circumferential direction as shown in FIG. 13A. This design provides tooth 101 with an overall greater circumferential width than the active teeth on cone 129 or the other cones. Moreover, the tapers may converge in a crest that is formed at multiple radii or non-uniform radii.

As shown in FIGS. 5 and 6, the anti-tracking feature 203 (e.g., a scallop) may extend between the two adjacent active teeth (i.e., the leading and trailing edges of the tooth 201) on one or more roller cones 229. The anti-tracking feature may also be formed more than once and in different locations on any tooth or combination of teeth. FIG. 13B depicts a top view of tooth 201. Anti-tracking feature 203 tapers not only radially from the crests or outer portions 205 with respect to the axis of cutter 129 (FIGS. 5 and 6), but also tapers toward the crest at 203 in the circumferential direction as shown in FIG. 13B. In some embodiments, this design also provides tooth 201 with an overall greater circumferential width than the other teeth on cone 229 or other cones. In other embodiments, however, the crests or outer portions 205 are configured to maintain the active tooth pitch on the row, essentially joining two adjacent active teeth with scallop 203.

Referring now to FIGS. 7 and 8, another embodiment of the invention comprises a heel row 301 having a higher count of anti-tracking teeth 303 (or, e.g., tungsten carbide inserts) on a roller cone 329 than other rows. The teeth 303 are configured at a projection 305 (i.e., in a radial direction relative to the axis of the cone) that is shorter than a projection 307 (shown superimposed) for teeth on the other roller cones. Although the radial height 305 of teeth 303 is relatively shorter than the active teeth, it is sufficiently long to break down formation build up left by other heel rows. As best shown in FIG. 7, the teeth 303 also may be provided with wear pads or weld pads 309 on their backs or outer surfaces (opposite the next row of teeth). For example, pads 309 may be provided at thicknesses such as 1/16^(th) to ⅛^(th) of an inch.

The proper difference in projection of teeth 303 from the active teeth may be varied according to the application. In addition, teeth 303 may be in any combination of 100% hardfacing material, hardfaced milled teeth, tungsten carbide inserts, etc.

Another embodiment of the invention for a drill bit 401 is depicted in FIGS. 9 and 10. In this version, an integrally-formed heel row 403 on a roller cone 405 comprises an anti-tracking element in the shape of a disk having a plurality of narrow slots 407 formed therein to define the plurality of anti-tracking teeth. In the embodiment shown, the slots 407 extend radially in a symmetrical configuration to define elongated teeth having properties and features as described above for the embodiments of FIGS. 2, 7, 8, etc.

One embodiment of an overall cutting profile for a bit constructed in accordance with the invention is shown in the superimposed view of FIG. 11. The cutting profile for each row of teeth is offset from the others. The lower block line 1101 is the profile or depth of cut of the active drilling elements 1103 (which are shown in solid lines). The upper block line 1105 is the profile of the anti-tracking (or, tracking limiter) features or teeth 1107 (which are shown in phantom lines), which extends into a range 1109 of the depth of cut 1101 of the active teeth. FIGS. 13C and D depict top views of some embodiments of anti-tracking teeth 1107, which may be aligned or offset with respect to the axis of the roller cone. In any row, the tracking limiter features can be added between active cutting elements. The bit, cone or an individual row may contain any combination of tracking limiter features. Moreover, the tracking limiter features need not be at the same height on each side as they transition to the active cutting elements.

As described above, FIGS. 11 and 12 show the relationship between the effective depth of cut of active cutting elements 1103 to the projection of the various embodiments of anti-tracking teeth. The radial height (see, e.g., line 1105) of the anti-tracking teeth 1107 projects or extends into the range 1109 of the effective depth of cut of the active teeth. The effective depth of cut is the distance “normal” teeth 1103 can penetrate the formation before adjacent teeth contact the formation.

If any cones share a common row position where the formation is generally removed by two cones, at least one cone could be populated with only the tracking limiter features. The shape of the active and/or tracking limiter features are not limited to traditional hardfaced radial teeth. The shapes of other either type could be any combination of pyramid, disk, non-hardened, hybrid, tungsten carbide inserts, etc.

This written description uses examples to disclose the invention, including the best mode, and also to enable those of ordinary skill in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention. 

1. A drill bit for reducing harmful effects of tracking, comprising: a bit body having bit legs with bearing pins; a roller cone mounted to each of the bearing pins to define a plurality of roller cones, each roller cone having an axis and rows of active teeth, each of the active teeth having a radial height, an outer end and an inner end that define a length, a pair of flanks that define a width and a crest at which the ends and flanks converge; spaces between the active teeth that define a depth of cut for the roller cones; and an anti-tracking element on at least one of the rows of active teeth and having a second radial height that is less than the radial height of the active teeth and extending into a range of the depth of cut, such that the anti-tracking element engages and removes formation that remains as a result of uncut formation left behind by the active teeth.
 2. A drill bit according to claim 1, wherein the anti-tracking element is in an outermost row of one of the roller cones.
 3. A drill bit according to claim 1, wherein the anti-tracking element has a crest with a width extending in a circumferential direction that is wider than the width of the active teeth.
 4. A drill bit according to claim 3, wherein the crest has a length in an axial direction that is less than an axial length of one of the active teeth.
 5. A drill bit according to claim 4, wherein the width of the crest of the anti-tracking element in the circumferential direction is greater than the length of the crest of the anti-tracking element.
 6. A drill bit according to claim 1, wherein the anti-tracking element comprises a plurality of anti-tracking elements located on more than one row of the plurality of roller cones.
 7. A drill bit according to claim 1, wherein the anti-tracking element comprises a heel row of a plurality of anti-tracking teeth having a higher count than any other row on the plurality of roller cones.
 8. A drill bit according to claim 7, wherein the plurality of anti-tracking teeth comprise tungsten carbide inserts.
 9. A drill bit according to claim 7, wherein the heel row comprises an integrally-formed anti-tracking element in a shape of disk having a plurality of slots formed therein to define the plurality of anti-tracking teeth, and the slots extend radially in a symmetrical configuration.
 10. A drill bit according to claim 7, wherein the plurality of anti-tracking teeth have wear pads on outer surfaces thereof opposite a next row of active teeth.
 11. A drill bit according to claim 1, wherein the anti-tracking element comprises a scallop extending between two adjacent active teeth.
 12. A drill bit according to claim 11, wherein the scallop tapers radially with respect to the axis of the roller cone, and tapers in width in a circumferential direction.
 13. A drill bit according to claim 11, wherein the anti-tracking element has a greater circumferential width than the active teeth, and crests of the anti-tracking element maintain an active tooth pitch on the row with other ones of the active teeth.
 14. A drill bit according to claim 1, wherein the anti-tracking element forms an integral portion of one of the active teeth and is curved on a leading or trailing edge of said one of the active teeth.
 15. A drill bit according to claim 14, wherein the anti-tracking element tapers radially with respect to the axis of the roller cone, tapers in width in a circumferential direction, such that the anti-tracking element has a greater circumferential width than the active teeth, and the tapers converge in a crest that is formed at multiple radii or non-uniform radii.
 16. A drill bit for reducing harmful effects of tracking, comprising: a bit body having bit legs with bearing pins; a roller cone mounted to each of the bearing pins to define a plurality of roller cones, each roller cone having an axis and rows of active teeth, each of the active teeth having a radial height, an outer end and an inner end that define a length, a pair of flanks that define a width and a crest at which the ends and flanks converge; spaces between the active teeth that define a depth of cut for the roller cones; and a plurality of anti-tracking elements located on more than one row of the plurality of roller cones, with at least one of the anti-tracking elements located on an outermost row of active teeth and having a second radial height that is less than the radial height of the active teeth and extending into a range of the depth of cut, such that the anti-tracking element engages and removes formation that remains as a result of uncut formation left behind by the active teeth.
 17. A drill bit according to claim 16, wherein the anti-tracking elements have crests with a width extending in a circumferential direction that is wider than the width of the active teeth.
 18. A drill bit according to claim 17, wherein the crest has a length in an axial direction that is less than the length of the active teeth, and the width of the crest of the anti-tracking element in the circumferential direction is greater than the length of the crest of the anti-tracking element.
 19. A drill bit according to claim 16, wherein the anti-tracking element comprises a heel row of a plurality of anti-tracking teeth having a higher count than any other row on the plurality of roller cones.
 20. A drill bit according to claim 19, wherein the plurality of anti-tracking teeth comprise tungsten carbide inserts.
 21. A drill bit according to claim 19, wherein the heel row comprises an integrally-formed anti-tracking element in a shape of a disk having a plurality of slots formed therein to define the plurality of anti-tracking teeth, the slots extend radially in a symmetrical configuration, and the anti-tracking teeth have wear pads on outer surfaces thereof opposite a next row of active teeth.
 22. A drill bit according to claim 16, wherein the anti-tracking element comprises a scallop extending between two adjacent active teeth.
 23. A drill bit according to claim 22, wherein the scallop tapers radially with respect to the axis of the roller cone, and tapers in width in a circumferential direction.
 24. A drill bit according to claim 23, wherein the anti-tracking elements have greater circumferential widths than the active teeth, and crests of the anti-tracking elements maintain an active tooth pitch on the row with other ones of the active teeth.
 25. A drill bit according to claim 16, wherein the anti-tracking element forms an integral portion of one of the active teeth and is curved on a leading or trailing edge of said one of the active teeth, the anti-tracking element tapers radially with respect to the axis of the roller cone, tapers in width in a circumferential direction, such that the anti-tracking element has a greater circumferential width than the active teeth, and the tapers converge in a crest that is formed at multiple radii or non-uniform radii. 